The invention relates to an improved packing assembly of the type used to prevent fluid leaks around a plunger. In a specific application, the packing assembly is used in plunger-type pumps.
In various well treating operations, such as hydraulic fracturing, fluids are pumped into the wellbore by plunger-type pumps, such as Triplex or Quintuplex pumps. On the suction stroke of the pump, each plunger is pulled along the plunger bore away from the valve chamber. At the end of the suction stroke, the plunger reverses direction and is pushed back along the bore toward the pump chamber, to displace incoming fluid through the outlet valves. Rings of packing material are installed in the plunger bore to prevent the incoming fluid from leaking past the plunger. Each of the packing rings, in cross-section, is shaped like a chevron, and each ring has a central groove on the front side which functions as a hinge. The rear of each packing ring, therefore, has a generally convex shape and the front face is of a generally concave shape. The bottom edge of each packing ring defines a lip which fits snugly against the plunger to provide the liquid-tight seal.
In one form of the packing assemblies now in use, the packing rings are set into the plunger bore in side-by-side relation. This structure is usually referred to as a single stack arrangement and generally includes about four packing rings. In front of the last packing ring in the stack is a metal (brass) female adaptor ring, a lubrication gland, a packing gland spacer, and a packing gland. The front face of the female adaptor ring has a generally concave shape, so that it can seat against the convex-shaped rear face of the first packing ring. Behind the first packing ring in the stack is a brass male adaptor ring. The rear face of the male adaptor ring has a generally convex shape, so that it can seat against the concave-shaped front face of the first packing ring.
Another arrangement of the packing rings is referred to as a double stack. This arrangement usually consists of two packing rings, with a female adaptor ring positioned in front of the last packing ring in the stack, a male adaptor ring positioned behind the first ring in the stack, and a male-female adaptor ring positioned between the two packing rings.
As the plunger moves back and forth in the plunger bore, on the suction and discharge strokes of the pump, the lips of the packing rings drag considerably. The adaptor rings keep the plunger concentric with the bore at the "fluid" end of the pump, and thus concentric with the packing rings. The adaptor rings also help to retain the integrity of the cross sectional dimensions of the packing rings. The adaptor rings now used in packing assemblies installed on plunger-type pumps have a serious defect which causes a wearing away of these rings, rather than increasing the life of the packing. For example, the concave-shaped front faces on the female adaptor rings now available are formed with a 90 degree angle, and the convex-shaped rear faces on the male adaptor rings are formed with either a 90 degree angle or an angle of 115 degrees. However, the packing rings now available have rear faces formed with an angle of either 110 degrees or 120 degrees, and the front faces of these rings form an angle of 90 degrees.
The big difference in the angle of the mating faces on the adaptor rings and the packing rings, makes it impossible to seat the adaptor rings snugly against the packing rings when the packing is installed in the plunger bore. In the packing assemblies now in use, therefore, there are wide gaps between the adaptor rings and the packing rings that allow the rings to wobble. This causes excessive wear on the packing as the plunger moves back and forth in the plunger bore. In some instances, the wear is severe enough to reduce the operating life of the packing to only a few hours.
In the practice of the present invention, the operating life of the packing is considerably improved by providing male and female adaptor rings with faces having an angle that precisely conforms to the corresponding angles formed on the faces of the various conventional packing rings now in use.